Added git preparation to Dockerfile.

Dockerfile

 FROM python:3.8-bullseye
 
+SHELL ["/bin/bash", "-c"]
+
 ########
 # Base #
 ########
@@ -14,6 +16,19 @@ RUN apt update && apt install -y nodejs npm aspell git
 
 RUN npm install -g markdownlint-cli markdown-link-check
 
+###########################################
+# prepare git for automatic merging in CI #
+###########################################
+RUN git config --global user.name 'Gitlab Bot'
+RUN git config --global user.email 'hpcsupport@zih.tu-dresden.de'
+
+RUN mkdir -p ~/.ssh
+
+#see output of `ssh-keyscan gitlab.hrz.tu-chemnitz.de`
+RUN echo $'# gitlab.hrz.tu-chemnitz.de:22 SSH-2.0-OpenSSH_7.4\n\
+gitlab.hrz.tu-chemnitz.de ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDNixJ1syD506jOtiLPxGhAXsNnVfweFfzseh9/WrNxbTgIhi09fLb5aZI2CfOOWIi4fQz07S+qGugChBs4lJenLYAu4b0IAnEv/n/Xnf7wITf/Wlba2VSKiXdDqbSmNbOQtbdBLNu1NSt+inFgrreaUxnIqvWX4pBDEEGBAgG9e2cteXjT/dHp4+vPExKEjM6Nsxw516Cqv5H1ZU7XUTHFUYQr0DoulykDoXU1i3odJqZFZQzcJQv/RrEzya/2bwaatzKfbgoZLlb18T2LjkP74b71DeFIQWV2e6e3vsNwl1NsvlInEcsSZB1TZP+mKke7JWiI6HW2IrlSaGqM8n4h\n\
+gitlab.hrz.tu-chemnitz.de ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIJ/cSNsKRPrfXCMjl+HsKrnrI3HgbCyKWiRa715S99BR\n' > ~/.ssh/known_hosts
+
 WORKDIR /docs
 
 CMD ["mkdocs", "build", "--verbose", "--strict"]